A coordinate cell-mediated immune response that includes virus-specific cytotoxic (CTL) as well as helper (HTL) T lymphocytes is likely to be an effective means of controlling viral replication in the setting of HIV infection. In the setting of viral suppression due to highly active anti- retroviral therapy (HAART), general immune function improves in many HIV-infected patients, yet HIV-specific CTL and HTL may decrease in number, presumably due to a decrease in antigen availability. We hypothesize that a therapeutic vaccine approach that targets conserved CTL and HTL epitopes may provide the most effective means of boosting and broadening HIV-specific immunity. Epitope-based vaccines offer the advantages of providing multiple conserved epitopes both dominant and subdominant, in a manner in which processing and presentation of those epitopes is optimized. However, HTL epitopes in HIV-1, and the CD4+ T cells that recognize them, remain poorly characterized. In order to design more effective vaccines that target HTL epitopes as well as to better understand the fate of the HIV-specific T helper cells during HIV infection, we propose to characterize responses against DR-super-motif HTL epitopes in conserved regions of HIV-1 proteins and to develop more sensitive methods of identifying and determining the specific function of CD4+ helper T cells. In Aim 1 we will evaluate frequency and cytokine profile of HIV HTL epitope-specific CD4+ T cells in several different HV-infected, patient populations that are candidates for therapeutic vaccines. In Aim 2 we will selectively expand and clone HIV- specific T cells from HIV-infected patient blood, and derive hybridomas expressing the antigen-specific T cell receptor. Using the information and tools developed in Aims 1 and 2, we propose to develop multi-meric soluble complexes tetramers of MHC class II molecules with HIV T helper epitope peptides in Aim 3. Lastly, in Aim 4 we will design and implement clinical trials of CTL and HTL epitope-based DNA vaccines in HIV- infected patients. The MHC class II-HIV peptide tetramers will be utilized to directly visualize HIV-specific CD4+ T cells and track them in infected patients, including the vaccine recipients in the proposed clinical trials. The results of these studies will not only facilitate the development of effective HIV vaccines and therapeutic approaches, but will also aid in our understanding of HIV immunopathogenesis.